1. Field of the Invention
This invention relates to an apparatus and method for determining the hematocrit reading of a blood sample and, more particularly, to the use of ultrasound to cause rapid separation of red blood cells from plasma in the blood sample, the separation being in the form of bands which provide a directly readable indication of the hematocrit of the blood sample.
2. The Prior Art
Hematocrit is a measure of the volume fraction that red blood cells occupy in the blood. Conventionally, hematocrit has been determined by subjecting a blood sample to very high gravitational forces in a high speed centrifuge apparatus for several minutes. The incrementally greater density differential of the red blood cells causes them to pack into the lower part of the sample holder under centrifugation.
A drop of blood is drawn by capillary action into a microhematocrit capillary tube, the end of which is then plugged with a clay-like material. Under centrifugation separation occurs with the red blood cells becoming packed into the lower end of the tube with the plasma being displaced toward the top of the tube. The hematocrit is calculated by determining the ratio of the length of the red blood cell volume to the total length of the blood sample times one hundred.
Blood loss, whether through trauma, gastrointestinal bleeding, or during surgery can be discovered promptly if the medical personnel have immediate access to hematocrit readings that are rapidly obtainable and accurate. Current methods of measuring hematocrit require five to ten minutes and involve access to the necessary centrifuge apparatus. Accordingly, emergency medical personnel such as civilian paramedics and military medics do not currently obtain hematocrit information in the field while treating trauma cases because a) the current method using centrifugation is time consuming and fairly labor intensive, and b) the required high speed centrifuge apparatus is a poor candidate for field use since it is expensive, bulky, heavy, and yet fragile.
Additionally, the treatment of a trauma or gastrointestinal bleeding case in a hospital is not satisfactory since even an emergency or "stat hematocrit" requires at least five minutes centrifugation in conjunction with significant technician time and labor. Due to the cost of the centrifugation apparatus they are also placed in centralized locations. The end result is an additional time increment is required (beyond the centrifugation time) to transfer the microhematocrit capillary tube containing the sample to the centrifuge and then transmit the resulting hematocrit reading back to the medical personnel. This time factor is further compromised severely by the fact that in an endeavor to save technician labor several samples will be collected over a period of time so that all these samples can be processed in the centrifugation apparatus at the same time.
In view of the foregoing it would be a significant advancement in the art to provide a fast, convenient apparatus and method for rapid determination of hematocrit. An even further advancement would be to have a rapid hematocrit that could easily become a commonly gathered patient parameter so that medical personnel could be alerted early to the medical needs of a trauma patient particularly in cases of internal bleeding. Advantageously, such a device could become a commonly carried physician tool so that the physician could obtain his own hematocrit reading instead of sending the blood sample to the lab and waiting to obtain the hematocrit reading therefrom. Such a novel apparatus and method is disclosed and claimed herein.